Climbing is a great sport for hackers. Each route up a wall presents a problem in need of solving -- and often, brute force won't help you.

You've really got to think through a route and learn the sequence of moves that'll get you to the top. And then, once you've got a route completely figured out, the gym changes it on you and throws a new problem in the way.

Highly recommended for people who like to work their brains while they exercise.